1. Field of the Invention
The present invention relates to wiring boards for mounting semiconductor components such as semiconductor integrated circuit chips (LSI chips) used for information processing devices such as computers.
In particular, the present invention relates to a wiring board with a decoupling capacitor used as a power supply provided in the vicinity of a semiconductor component, which allows the semiconductor component to operate stably and speedily, and a semiconductor device comprising the wiring board and semiconductor component mounted thereon.
2. Description of the Related Art
Conventionally, in order to operate a semiconductor component speedily and stably, studies have been devoted to stabilizing supply potential and ground potential to the semiconductor component by disposing the so-called decoupling capacitor in the vicinity of the semiconductor component so as to stably supply power to the semiconductor component and suppress power supply noise.
As the wiring distance for electrically connecting the decoupling capacitor and semiconductor component lengthens, due to the resistance and inductance that the wiring has, it becomes difficult to maintain power supply potential and ground potential stably.
In order to dispose the decoupling capacitor in the nearest vicinity of the semiconductor component, there has been proposed a structure in which, for example, the wiring board is fabricated by a ceramic multilayer technique, and the power supply wiring and ground wiring stacked among the dielectric layers are arranged in a sheet-like manner so as to generate capacitance among them, and a decoupling capacitor is disposed inside the wiring board.
However, although the approach for forming a decoupling capacitor by utilizing conductive layers and dielectric layers allows the wiring distance to be shortened, because of small dielectric constant of the dielectric layers, it has the drawback that the capacitance is insufficient compared to when a chip capacitor is used.
Also, there is an existing method in which a chip capacitor is disposed on the back side of the semiconductor component-mounting area of the wiring board to shorten the wiring distance by wiring that penetrates the wiring board.
In this method in which electrical connection is made by the wiring that penetrates the wiring board, while capacitance is sufficient because of the use of the chip capacitor, the wiring distance is prolonged by the thickened wiring board and inductance of the wiring inside the wiring board becomes too great to be negligible.
In order to further shorten the wiring distance, there have been proposed structures including the following: a structure in which a chip capacitor is buried inside the wiring board; a structure in which a chip capacitor is embedded in a cavity formed in the surface of the wiring board; and further, a structure in which a chip capacitor is disposed in a gap between the wiring board and a semiconductor component mounted thereon.
However, when the structure in which the chip capacitor is buried inside the wiring board is employed, peeling, cracking or break due to difference in thermal expansion coefficient between the buried chip capacitor and the material of the wiring board around the chip capacitor, and break due to clearance caused by insufficient machining accuracy on the wiring board and chip capacitor would occur.
Also, when the structure in which the chip capacitor is embedded in the cavity formed on the surface of the wiring board, because the bottom surface of the cavity for embedding the chip capacitor reaches inside the wiring board, the structure does not allow the capacitor to directly connect to a conductive wiring layer on the surface of the wiring board, and the connection is made via a conductive wiring layer on the back side of the wiring board. As a result, the wiring distance lengthens.
Although the method in which a chip capacitor is disposed in a clearance between the wiring board and a semiconductor component allows short wiring distance and high mounting accuracy, space for inserting the chip capacitor between the wiring board and the semiconductor component is necessary. The distance of this needs to be at least greater than the thickness of the chip capacitor, which is considerably large as compared to the height of a solder bump in the currently mainstream flip-chip mounting. Thus, realistically, inserting a chip capacitor is difficult, and this method can be applied to only limited applications that permit a large bump pitch.
It is an object of the present invention to provide a wiring board and a semiconductor device capable of effectively and stably supplying power and suppressing power supply noise that are necessary for stably operating semiconductor components.